This invention is concerned with improvement in tightening tool for threaded screw part such as screw driver, and so forth. It has heretofore been considered advantageous for increasing working efficiency in continuous tightening operation of threaded screw part, if the tip end of the engagement part of a box spanner or a screw driver, for example, is once fitted onto a head of a bolt, or inserted into a groove of a small screw so as to firmly hold such bolt and screw by the tip end of the engagement part for the subsequent carrying out of the screw tightening work.
There has so far been known a tool of a type, wherein a spring is provided at the tip end of the engagement part of the abovementioned tool with a view to holding a threaded screw part at the tip engagement part by the elastic force of the spring. However, as this known type of the screw tightening tool is rather complicated in its structure for the spring fitting, the manufacturing cost would become high, and, moreover, it has had such a disadvantage that, when the elastic force of the spring has become weakened after repeated tightening operation over a long period of time, exchange of the spring cannot be effected at ease. Also, such tightening tool that is simple in its fitting structure, particularly, such one wherein a plate spring is fixed by a rivet to the main body of the tightening tool per se, cannot be repaired at the users themselves, but must be returned to the manufacturer or dealer at every time the repairing has become necessary. This is highly uneconomical.